Method of and apparatus for segregating by fractional solidification



Oct. 24, 1961 K. F. GRIFFITHS METHOD OF AND APPARATUS FOR SEGREGATING BY FRACTIONAL SOLIDIFICATION 5 Sheets-Sheet 1 Filed June 22, 1959 J C a i: ww o 0 at: o mm m ase 0 E f f v S A G D O R E F G u in 0 u T A 6 m i F F m .L 0 S P 0 000 O T ll!!! ONO 00600 N o o 00 E II 00 9 o o v 0 0 00 o S w A G c s END OF SOLIDIFICATION PERIOD SOLID MATERAL vllln I FLUIDIZATION PERIOD SC-l CONCENTRATED IMPURITY 2 r S 0 m @0 0 m u 0 w 0% R E I' P I. N MN .m 0 GM flue m 0 1 F U Q L O C F @O F o M w w N OD E 0% m P %%o ww m o 0 mi l c S PURlFlED MAJOR FLUID INVENTOR. Kenneth F.G 'ffiths BY ATTORNEY Oct. 24, 1961 K. F. GRIFFITHS 3,005,691

METHOD OF AND APPARATUS FOR SEGREGATING BY FRACTIONAL SOLIDIFICATION Filed June 22, 1959 5 Sheets-Sheet 3 12 Z 19$ FIG-6 21 132921 as 24 :30 252 2a 20 11 20 230 21 29@ (I ZQ3OFIG.7

29 2 l5 INVENTOR. 30% 1 3 Kenneth F.Griffiths 1232 W BY ATTOR N 3,fitl5,691 METHOD OF AND APPARATUS FQR SEGREGAT- ING BY FRACTIQNAL SOLHDIFICATION Kenneth F. Grifiiths, Newark, NJ. (201 Bloomfield Ave, Verona, NJ), assignor of fifty percent to John L. Kerby, Larchmont, N.Y.

Filed June 22, 1959, Ser. No. 822,064 58 Claims. (Cl. 23-295) This invention relates to fractional solidification and is particularly concerned with a method and apparatus for treating fluid materials on either a continuous or batch-type basis whereby the ingredients making up the material can be segregated so that one ingredient (e.g. a major ingredient) can be separated from one or more other ingredients (e.g. minor ingredients).

The term fractional solidification as used herein is meant to include fractional freezing, fractional crystallization and fractional sublimation.

It is known that fractional solidification, etg. fraction freezing, may be employed to segregate a major ingredient from a minor ingredient in cases in which the solubility of the minor ingredient is different in the solid than the liquid phase of the major ingredient. For example, if a portion of a given quantity of a liquid mixture of a major and a minor ingredient is frozen and the coefficient of solubility of the minor ingredient in the solid phase is less than in the liquid phase of the major ingredient, the concentration of the minor ingredient would be less in the solidified portion of the major ingredient than in the liquid portion.

Likewise, it is known that fractional crystallization can be employed to segregate a minor solute from a major solute dissolved in a suitable solvent in cases in which the ratio of the major ingredient to the minor ingredient is different in the solid than the liquid phase on the liquid solid crystallization interface. A portion of the solutes can be caused to crystallize out of a saturated solution by lowering the temperature of the solution in cases in which the coeilicient of solubility of the solute increases with increasing temperature; by raising the temperature of the solution in cases in which the coefficient of solubility of the solute decreases with temperature; or by evaporating part of the solvent from the solution. Solid solute crystals can be caused to dissolve into a saturated solution of the solute by raising the temperature of the solution in cases in which the coefficient of solubility of the solute increases with rising temperature; by lowering the temperature of the solution in cases in which the coeflflcient of solubility of the solute decreases with increasing temperature; or by adding pure solvent to the solution.

When fractional crystallization is being conducted, the concentration of the major ingredient in the solution must be such that its crystallization temperature from solution is higher than the freezing point temperature of the solvent from the solution.

Fractional sublimation may be employed to segregate a relatively volatile substance from a relatively less volatile substance in cases in which a portion of a mass of gas comprised of a major ingredient and at least one minor ingredient is partially condensed at a pressure less than the vapor pressure of the major ingredient at its melting point temperature. After a portion of the gas has condensed, the percentage concentration of the relatively less volatile ingredient in the solid phase is more than in the gas phase. Also, the percentage concentration of the more volatile ingredient in the gas phase is higher than in the solid phase on the gas-solid condensing interface.

It would be desirable if the foregoing types of fractional solidification could be carried out efiiciently and economically on a continuous basis. A continuous proc- 3,005,691 Patented Oct. 24, 1961 ess has been proposed for fractional freezing based on the well known zone refining technique employed in the purification of semi-conductors for use as transistor components. material is provided and a portion of it heated to form a molten zone which is caused to traverse from one end to the other of a column of material being zone refined. The result is that the impurities that are more soluble in the liquid than the solid phase of the major ingredient are concentrated in the end of the column towards which the liquid-solid interfaces move, and the impurities which are more soluble in the solid than the liquid phase of the major ingredient are concentrated in the other end. In effect, the liquid zone acts as a thermodynamic broom in sweeping the impurities to one end of the column. My present method is analogous to zone refining in the final result but it accomplishes the result in a different manner.

A disadvantage of zone refining is that it is not applicable to conducting zone crystallization because the solvent acts as a minor ingredient and is swept to the impure end of the column of material being purified. If solvent is introduced to the end of the zone refining column from which the liquid-solid interfaces move, the net result is that all the material in the zone refining column goes into solution after a certain quantity of solvent has traversed the column. My invention overcomes this disadvantage as will be apparent hereinafter.

It is an object of my invention to provide a fractional solidification process having the advantages of zone refining but which is applicable to fractional freezing, fractional crystallization and fractional sublimation.

An additional object of my invention is to provide a simple method of conducting continuous fractional crystallization in which a substantially saturated feed solution of an impure major ingredient is introduced continuously at or near the central portion of a fractional crystallization column, a solution of purified major ingredient is continuously withdrawn from the pure end of the column, and an impure solution of the major ingredient (containing substantially all the impurities introduced with the feed) is withdrawn from the impure end.

Still another object of my invention is to provide a simple method of conducting continuous fractional freezing in which a molten impure major ingredient is continuously fed to or near the central portion of a fractional freezing column, molten relatively pure major ingred' ient is continuously withdrawn from the pure end of the column, and relatively impure major ingredient containing substantially all the impurities introduced in the feed is continuously withdrawn from the impure end.

A further object of my invention is to conduct continuous fractional sublimation wherein either a gaseous or solid impure major ingredient is continuously fed to or near the central portion of a fractional sublimation column, gaseous relatively pure major ingredient is continuously withdrawn from the pure end of the column, and relatively concentrated gaseous impurities is continuously withdrawn from the impure end of the column.

Another object of my invention is to provide an inexpensive method of segregating a relatively pure solvent from a solution in which the solute concentration is low enough such that the crystallization temperature of the solute is below the freezing point of the solvent from the solution. Therefore, my invention can be employed for the recovery of fresh water from sea water.

A further object of my invention is to provide a method for effecting sharp separations of substances that are hard to separate by ordinary zone refining, fractional crystallization or fractional sublimation procedures.

An additional object of my invention is to provide a method whereby fractional solidification can be conducted with high thermal efficiency.

In this refining process, a column of fusible of the method employed in carrying out my invention;

FIG. 2 depicts diagrammatically three embodiments of themethod which may be employed in carrying out my invention;

FIGS. 3,4 and show various views of one type of fractional solidification apparatus employed in carrying out the invention, wherein FIG. 3 is across section taken along line 33 .of FIGS, FIG. 4 is a cross section taken along line 4-4 of FIG. '3 and- FIG. 5 is across section taken along line 5-5 of FIG. 3; FIG. 6 illustrates somewhat schematically another type "of apparatus similar in its operation to the apparatus illustrated in FIGS. 3 to 5; and

FIG. 7 depicts schematically still another type 0f fractional solidification apparatus having particular use for fractional sublimation. V

Broadly stated, my fractional solidification treatment comprises establishing a long column of material which -may be horizontahvertical or inclined, comprised of at least two ingredients, for example, a major ingredient and one or more minor ingredients, and subjecting'said material to a solidification and fiuidization cycle, during whichcycle the material in the fluid state is caused to new in sequentialrelationship towards one end of the colunm.during a'portion of the cycle and then towards the other end of the column during another portion of the cycle, whereby segregation of one'ingredient from another is effected. The column, for reference purposes, is characterized by a major end to which the major ingredient is transposed and a minor end to which the one ;or more minor ingredients are transposed. During each cycle, when fluid material is transported towards the minor end of the column, at least a portion of the material in the column is in thesolid state; whereas when fluid material is transported towards the major end of the column, substantially all of the material in the column is in the fluid state.

. In carrying out my fractional solidification process, the column of material is caused to undergo a series of repeated cycles in which eachcycle is comprised of at least the following periods: i

(1) There is at least one minor flow period in which: (A) A lower. percentage of the. major ingredient in the column is in the fluid (liquid or gas) state during the minor flow period than during the major flow period; 7 (B) The major ingredient in the column that is in the fluid state during the minor flow period flows a given distance towards the minor end of the column. (2) There is at least one major flow period in which: (A) A higher percentage of the majoringredient in the column is in the fluid state during the major flow period than during/the minorflow period; '(B) The major ingredient in the column that is in the fluid state during the major flow period flows a given distance towards the major end of the column.

At the end of the major flow period of each cycle, the position of the body'of material in the column is substantially the same as at the beginning of the minor flow period. a

When'a fractional soldification column is being operated, the impurities are transported to either the major or the minor end of the column. It is to be understood that the term impurities as used herein is not meant to be limited to undesirable ingredients, since an impurity may be desirable or undesirable depending upon whether it or the major ingredient or both are the subjects of the recovery or purification treatment.

In cases in which the ratio of the concentration of minor ingredient to major ingredient is higher in the fluid than in the solid state of the major ingredient on the fluid-solid solidification inter-face, the pure end of the column corresponds with the major end and the impurities (minor ingredient) are driven to the minor end. In cases in which the ratio of the concentration of the minor ingredient to the major ingredient is lower in the fluid than in the solid state of the major ingredient on the fluidsolid interface, the pure end of the column corresponds with the minor end and the impurities (minor ingredient) are driven to the major end.

In all cases, the segregation coefficient k" must be either more or less than unity. In other words, segragation of at least one minor ingredient from the major ingredient must be effected at the fluid-solid solidification interface. .For example, when the segregation coeflicient'k" is less than unity, the ratio of minor to major ingredient is higher in the fluid than the solid phase at the fluid-solid solidification interface.

In my fractional solidification process, the solid major ingredient in the column is contemplated as remaining stationary with respect to the side walls of the column. In cases in which a slush forms during the solidification periods, the slush should remain in a relatively stationary position while the remaining liquid is moved.

In my fractional'solidification process, the major ingredient may be caused to go from the fluid to the solid state by either withdrawing heat from the column, adding heat to the column, changing the pressure in the column or by evaporating solvent from the column. More specifically, at least some of the major ingredient in the column may be caused to go from the fluid to the solid state in the following manners:

(1) When my fractional solidification process is being operated as a fractional freezing process, a desired amount of liquid major ingredient may be caused to freeze in the column by withdrawing heat from the column;

(2) When my fractional solidification process is being operated as a fractional crystallization process, a desired amount of major ingredient solute may be caused to crystallize by:

(A) Evaporating some column;

(B) Extracting heat fromthe column in cases in which the coefiicient of solubility of the major ingredient increases with increasing temperature;

(C) Adding heat to the column in cases in which the coefficient of solubility of the major ingredient increases with decreasing temperatures;

(3) When my fractional solidification process is being operated as a fractional sublimation process, a desired amount of gaseous major ingredient may be caused to condense in the column by either increasing the pressure or more often by withdrawing heat from the column.

of the solvent from the More specifically, the fractional solidification column can be operated with the following four steps in each cycle:

(1) A portion (usually about half) of the major ingredient is caused to solidify in the column;

(2) After the solidification period, the major ingredient remaining in the fluid state is moved a given distance towards the minorend of the column;

(3) After the minor flow period; the solidified maior ingredient is caused to go from the solid to the liquid phase;

(4) After the fluidization period, the fluid major ingredicut is moved a given distance towards the major end of the column during the major flow period.

The foregoing will more clearly appear by referring to the simple graphical illustration shown in FIGS. 1a to ld which show a horizontal column connected at the extreme ends to surge chambers SC-l at the major end of the column (Ma) and SC-2 at the minor end (Mi). The column is filled with fluid material represented by white and black circles which may, for example, be sea water, the white circles being the major ingredient water (solvent), the black circles being the minor ingredient salt (solute). Surge chamber SC-l is fluidly coupled to the major end of the column while chamber SC-Z is fluidly coupled to the coupled to the minor end.

The bottom of the column is cooled by refrigeration and FIG. la shows it at the beginning of a freezing period of a cycle. At the end of the freezing period, the major ingredient (fresh water) has segregated out of the solution as ice as shown by the shaded area along the bottom of the column in FIG. 1b which shows the solid major ingredient as white circles. At this point in the cycle a given quantity of water is pumped from chamber SC1 into the pure end (major end) of the column thereby causing the remaining fluid in the column to flow a given distance towards the minor end of the column.

At the same time a given quantity of water is allowed to flow from the impure end (minor end) of the column into chamber SC2. It will be noted from FIG. 1b that the minor ingredient (black circles) is more concentrated at the right hand end than the left hand end of the column.

The solid major ingredient is then subjected to fluidizetion or melting (FIG. is) by applying heat to the column whereby the ice melts. At the end of the fluidization period, a given quantity of liquid is pumped from surge chamber SC-2 into the impure end of the column causing flow of the fluid in the column a given distance towards the major or pure end of the column, whereby the fluid material is brought back to the same position it occupied during the period illustrated in FIG. la, with the exception that the major end of the column (Ma) is now more enriched in the major ingredient when we assume that the cycle shown in FIG. 1 shows the operation of a cycle at the start of a run before the ingredients in the column have had the opportunity to achieve an ultimate distribution. However, if the apparatus had been operating for enough complete cycles in a run to have allowed an ultimate distribution of impurities (salt) to have established itself along the column, the concentration of salt in any given portion of the column would be the same in FIG. 1a and FIG. 1d. This is analogous to a batch type zone refiner operating after an ultimate distribution of impurities has been achieved in it.

It is assumed that at the start of each cycle, substantially all the major ingredient is in the fluid state. During the fluidization and the solidification periods, the fluid material in the column may be held stationary or may be moved at a controlled rate in a manner to be described below.

I have discovered that the efficiency of my fractional solidification process is at its highest possible level if the control of the motion of fluid material in the fractional solidification column during the fiuidization and solidification periods is such that the ratio of the concentration of the major and the minor ingredients in the liquid phase be maintained the same as in the solid phase of the major ingredient on the fluid-solid fluidization interface during the fluidization period. For example, at a given distance from the impure end of the column, it is desirable that while the solidified portion of the major ingredient is melting, the concentration of impurities in the liquid at the liquid-solid melting interface is the same as in the solid at that interface. This desirable condition may be achieved best by the following methods A, B and a combination of methods A and B (method C). These three methods are illustrated diagrammatically in FIG. 2. Assuming that each cycle starts with all the major ingredient in the fluid state, each cycle of method A may be operated in the following manner:

(1) During the solidification period of each cycle, the fluid major ingredient is moved at such a rate. towards the minor end of the column that the ratio of minor ingredient to major ingredient in the solid phase on the fluid-solid interface in any given portion of the column remains substantially the same during the entire solidification period. For example, at a given distance (say meters) from the impure end of the column. The material frozen there at the beginning of a given solidification period would have the same concentration of impurities as the material frozen there at the end of that given period. Also, the material frozen in that same given solidification period at a distance of say 50 meters from the impure end of the column would have a higher concentration of impurities than that frozen 100 meters from the impure end. After the conclusion of the given solidification period, the concentration of impurities is greatest at the impure end of the column and diminishes as one would go towards the pure end. This desirable condition can be achieved by controlling both the rate of solidification and the rate of fluid motion in the column throughout the entire solidification period.

(2) At the conclusion of the solidification period of each cycle, the remaining fluid is moved towards the minor end of the column a distance such that at the conclusion of the motion the ratio of the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface. Note: if all the liquid is frozen in step 1 (solidification period) then step 2 (minor flow period) may be eliminated.

(3) During the fluidization period of each cycle, the fluid major ingredient is held stationary in the column.

(4) At the conclusion of the fluidization period, the major ingredient fluid is moved towards the major end of the column a distance such that its position is the same as at the beginning of step one.

Referring to FIG. 2, method A is shown comprising steps AG) to A(4). In A(l) the column is shown diagrammatically as a horizontal line having a major end Ma and a minor end Mi with a central feed designated by F. The surge chambers illustrated in FIGS. la to ld are not shown. During solidification, the fluid is caused to flow towards the minor end at a rate such as to maintain a constant concentration of impurities in the liquid phase on the solidification interface at the feed point P or any other given point in the column during the entire 7 solidification period. At the end of the solidification period (A-Z), the remaining fluid is moved towards the minor end Mi a distance such that the concentration of impurities is substantially the same in the liquid and the solid phase of the major ingredient on the liquid-solid interface at any given point in the column such as the feed point F. The material in the column is held stationary during the fluidization period (A-3). At the end of the flu-idization period (A 4), the fluid in the column is caused to flow a sufficient distance towards the major end of the column to bring it to the same position it occupied at the beginning of the solidification period (A-l When method A is operated as a continuous process, a flow of feed can be introduced into the central portion of the column at point F, product (P) can be Withdrawn at the major (pure) end (Ma) and by-product (ByP) can be withdrawn at the minor (impure) and (Mi). The flow of product from feed point P to the major end (Ma) and of by-product from feed point F to the minor end (Mi) may be superimposed on the controlled flow of fluid through the column during the minor flow period represented in A-2 or the major flow period represented in A-4. In continuous operation of the process-shown in method A of FIG. 2, a steady state would be reached after a number of cycles whereby the product withdrawn from the major end would remain at a given purity which would be higher than that of the feed, and the byproduct would contain a higher concentration of impurities than the feed.

In carrying out method B, the same assumption is made that each cycle starts with all the major ingredient in the fluid state, each cycle being operated in accordance with FIG. 2 in the following manner:

(1) The fluid major ingredient in the column is held stationary during the solidification period as shown by 13(1).

(2) At the end of the solidification period of each cycle B(2), the fluid is moved towards the minor end of the column a distance such that at the conclusion of the motion the ratio or" the concentration of'the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface. Note: If all the liquid is frozen in step 1 (solidification period), then step 2 (minor flow period) can be'eliminated.

(3) During the fluidizing period of each cycle 3(3), the fluid is moved towards the minor end of the column at a rate such that the ratio of the minor ingredient to the major ingredient remains the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface. This would require a control of both the melting rate and the flow rate of fluid towards the minor end of the column during the entire fluidization period. A1so, the solid should be melted, dissolved or vaporized from the opposite side from which it was solidified. For example, if the column were horizontal and the solid were frozen upward from the floor of the column during the solidification periods, it would be melted from the top downward during the fluidization periods.

(4) At the conclusion of the fluidizing period B(4), the fluid major ingredient is moved towards the major end of the column a given distance such that its position is the same as at the beginning of step one.

As in method A, feed can be introduced at F, product can be withdrawn at the major end (Ma) and by-product can be withdrawn from the minor end (Mi).

Assuming that each cycle starts with all the major ingredient in the fluid state, each clycle of a combination method of A and B (referred to as method C) may be operated in the following manner:

(1) During the solidification period of each cycle C(l), the major ingredient fluid is moved at a controlled rate towards the minor end of the column. However, in most cases it is not moved as fast as in step ('1) of method A. i

(2) At the end of the solidification period of each cycle C(12), the fluid is moved towards the minor end of the column a distance such that at the conclusion of the motion the ratio of the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface. Note: If all the liquid is frozen in step 1 (solidification period) then step 2 (minor flow period) can be eliminated.

'(3) During th e fluidization period of each cycle, the major ingredient fluid is moved towards the minor end' of the column at a rate such that theratio of the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface. This would require a'control of the melting rate, the duration'of melting and the flow rate of the liquid through the column during the fluidization period. 7

' (4) At theend of the fluidization period, the major ingredient fluid is moved a given distance and direction in thecolumn such that its position is the same as at the beginning of step one. In this step it may be required to move the fluid either to Ma or Mi depending upon the amount of movement of steps C(l) to C(3).

What has been said regarding methods A and B concerning continuous introduction of feed and withdrawal of product and byproduct would hold also for this method.

The common factors of method A, B and combinations of methods A and B (i.e. method C) are as follows:

(1) During the solidification period of each cycle, the major ingredient fluid may be moved at a controlled rate with respect to the minor and the major end of the column or may be held stationary.

(2) At the end of the solidification period, the fluid may be moved towards the minor end of the column a distance such that at the completion of the motion the ratio of the minor ingredient to the major ingredient is the same in the fluid and in the solid phase of the major ingredient at any given point on the fluid-solid interface. Note: The only exception to this is when all the material in the column is solidified in the solidification periods.

(3) During the fiuidization period of each cycle, the fluid is moved with respect to the solid material in the column at such a rate that the ratio of the minor ingredient to the major ingredient remains substantially the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface.

(4) At the end of the fluidization period, the fluid is moved in such a direction with respect to the ends of the column that it ends up in the same position as it occupied at the beginning of the solidification period.

If no material is added to or withdrawn from the fractional solidification column while my fractional solidification process is in operation, the process would be operated on a batch-type basis. However, as stated above, the process can be made continuous by the introduction of liquid feed tothe central portion of the column, by the withdrawal of purified material from the pure end of the column, and by the withdrawal of relatively impure material from the impure end of the column.

During continuous operation, material may be with drawn from or admitted to the fractional solidification column either at a constant rate or a variable rate. Since in mose casm a portion of the interior bore of the column is fluid at all times during the operation of the process, there is free passage of fluid material from the feed point to each end of the column.

When the process is being operated on a continuous basis, the flow rate of product through the impurity stripping section from the feed point to the pure end should not be greatenough to transport impurities towards the pure end as fast as the action of the process tends to transport them in the opposite direction in the impurity stripping section. In many cases, the flow rate of prodnot is selected such that the ability of the process to carry. impurities toward the feed point in the impurity stripping section is approximately twice as great as the ability of the motion of the feed to carry impurities in the opposite direction in this section; therefore, the net result is that the flow of teed is stripped of impurities as it flows through the impurity stripping section. Where a pure product is required, the ratio of the flow rates of the impure by-product to feed must be at least as great as the ratio of the allowable concentration of impurities in the by-product to their concentration in the feed. For example, if the greatest allowable concentration of impurity (minor ingredient) were one part in ten and the feed contained one part of minor ingredient in 50 parts of feed, the flow rate of by-product would have to be more than 20% of that of the feed. If the by-product flow rate were less than 20% of that of the feed, all

the impurities could not leave the impure end of the column and the byproduct would contain the maximum allowable concentration of impurities, i.e, impurity concentration. In this example, the mixture of 10% minor ingredient and 90% major ingredient may be equal to either an eutectic or a paraeutectic composition of those two ingredients. When the process is operated as a fractional freezing process, the highest allowable concentration of impurities in the by-product may be defined by the eutectic or a paraeutectic composition of the impurities and the major ingredient. When the process is operated as a fractional crystallization process, the highest allowable concentration of impurities in the by-product may be defined as the ratio of major to minor ingredient solute which is rich enough in impurities to cause the ratio of major and minor ingredient on the crystallizing interface to be the same in the liquid and the solid phase. When the process is operated as a fractional sublimation process, the highest allowable concentration of minor ingredient in the by-product is 100% concentration.

In cases in which heating and cooling of the contents of the column is employed to cause a portion of the major ingraedient to change phase, I have found that the process is easier to operate when the column is provided with separate heating and cooling means. For example, one side of the column could be heated during the heating period and the opposite side could be cooled during the cooling period. When the heating of the column is carried out in this manner, the heat cm go directly from the heating surface into the liquid or gas material without first having to go through a layer of solidified material. If heat were both withdrawn from and added to the material in the column from the same source, the heat would have to go through a layer of solidified material before reaching the liquid-solid or gas-solid interface. Also, in many cases it is desirable that the solidified material melt, dissolve or sublime in inverse order to how it froze, crystallized or condensed.

In all cases in which the process is operated, I prefer that the material is solidified in such a manner that a minimum quantity of liquid is trapped or occluded within the solid.

I have found that my fractional solidification process works best when heat is applied to the contents of the fractional solidification column during each heating period in such a manner that every centimeter of length of the column receives an amount of heat equal to the mass of material within that centimeter. This can be done easily by heating the entire contents of the column to a uniform controlled temperature. For example, steam condensing at a controlled pressure can heat the entire column to a uniform controlled temperature. Likewise, I have found that it is best to remove heat from the contents of the fractional solidification column during each cooling period in such a manner that every centimeter of length of the column loses the same amount of heat that it received during the beating period before it. This may be done by chilling one side of the column to a uniform temperature low enough to cause solidification and by employing a column of uniform cross sectional shape and area normal to its longitudinal axis. Also, this may be accomplished by having heat withdrawn from one side of the column to a heat sink of uniform temperature through a layer of material of constant heat conducting ability, thereby enabling a controlled rate of heat flow per unit area of wall from the interior of the column to the heat sink. When such a uniform heat conducting layer is employed, I prefer that it be designed to have the lowest heat capacity possible. The duration of the solidification period would control the amount of heat last from the column.

I prefer that the material in the column be so distributed in it that every centimeter of length of the column has the same quantity of material. For example, every centimeter of length of the column could contain grams of material. This way all the fluid material moving in the column would travel at the same velocity with respect to the solid major ingredient adhering to the walls.

Broadly speaking, the apparatus employed in carrying out my invention may assume many difierent kinds of shapes and forms and still be useful for my fractional solidification process. For example, the column may be a straight tube, a conduit having many bends, a spiral or any shape that allows the column to have a high length to width ratio. In some cases, the column may be comprised of a row of chambers which are connected in series by a suitable conduit. I prefer that the length to width ratio of the column be quite high with the upper limit usually being governed by the consideration of excessive pressure being required to drive fluid through the column during the flow periods. I have found that the longer and thinner the column, the less is the undesirable effect of back diffusion of impurities towards the pure end. However, I have also noticed that the longer and thinner the column, the higher is the pressure required to drive the liquid through it during the flow periods. Therefore, the length to width ratio of the column is usually a compromise between the pressure required to force fluid through it and the undesirable effect of back diffusion of impurities. In cases in which the column consists of a series of chambers, the effect of back diffusion can be minimized by having the conduit which connects each chamber with its neighboring chamber be relatively narrow.

There are many different methods of supplying heat to the contents of the column and withdrawing heat from them. In some cases, heat may be put into the column through the column side walls alongd a longitudinal element thereof and be withdrawn from the column through the side walls. In some of such cases, the heat may be put into the column during the heating periods through a different portion of the side walls than the portion of those walls from which heat is withdrawn during the cooling periods. In some cases, such as when my process is employed for fractional sublimation, the contents of the column may be heated during the heating periods by one or more immersion heaters placed within the column; and, the contents of the column may be chilled during the cooling periods by one or more immersion coolers placed within the column.

It should be understood that my fractional solidification process may often be operated with a pair of fractional solidification columns. The material in one of the columns may be heated while the material in the other one is being chilled and vice versa. With such an arrangement, a heat pump system may be employed to extract heat from the column being chilled and dump it at a higher temperature into the column being heated.

In its broad aspects, the apparatus of the invention is comprised of a horizontal or vertical or inclined column which defines an elongated chamber having a major end to which the major ingredient is segregated and a minor end to which the minor ingredient is similarly segregated. The column has associated with it means for solidifying a portion of the fluid material during a step of a treating cycle and also means for fluidizing the material during another step of the treating cycle. The ends of the column each have associated therewith fluid coupling means with which fluid driving means cooperate to effect sequentially the movement of fluid in the column in one direction during or after solidification is complete and then in the opposite direction at another treating step during or after fiuidization is complete. Thus, when the material is returned to substantially its original position in the column, the major end of the column is enriched in the major ingredient and the minor end enriched in the'minor' ingredient. apparatus would beapplicable to a batch type process The foregoing but can be converted for continuous operation by providing material-feed means at the central part. of the column and discharge means at the major and minor ends.

As illustrative of several of the various apparatus embodiments which may be employed in carrying out '15 could serve as condensing and evaporating chambers,

respectively, as part of a refrigeration system in which relatively high pressure gas from the high pressure side of the compressor would be condensed in the condensation chamber during each of the fiuidization periods and relatively low presure liquid refrigerant would be evaporated from the evaporation chamber during the solidification periods. During each of the fiuidization periods, the high pressure gas could enter condensation chamber 14 through conduit 17 and the condensate could leave chamber 14 through this same conduit '17 by gravity flow. During each of the solidification periods, the low pressure condensate can enter chamber 15 by gravity flow through conduit 16 and the vapor can leave chamber 15 through that same conduit 16. The level floor of chamber d can be flooded to a uniform depth to insure that all its portions are cooled to a uniform temperature during the solidification period. The rate of heat transfer through the floor of the evaporation chamber can be controlled by the pressure maintained in its; the lower the pressure the lowerthe temperature and the faster the heat flow from the solidifying material. During each solidification period, as the thickness of solidifying material under and adjacent to the evaporation chamber becomes greater, the'pressure and the temperature of that chamber can be lowered to compensate for the increased thermal resistance of the solid material; If desirable the proper programming of the pressure in the evaporation chamber can be such that a constant thermal flux, and consequently a constant solidification rate can be maintained during the entire solidification period.

The apparatus shown in FIGS. 3, 4 and 5 has a feed conduit 11, a discharge conduit 12 for the product and a discharge conduit 13 for the by-product. At the product end 19 of the fractional solidification column a surge chamber tank 27 for pure liquid is provided and is connected to end 19 by means of conduit 29. At the byproduct end 21a reversible proportioning .pump may be provided and be in such a position that it can pump in pure liquid from end 21 into tank 24 or in the opposite direction. Tanks 24 and 27 may be provided with vent conduits to the atmosphere or some other suitable source of inert gas. p r

The foregoing apparatus may be used to purify an impure molten material, such as certain of the low melting metals, or liquid solutions such as sea water. The operation of the process maybe effected by filling column 20 with a liquid, such as naphthalene. Surge chamber 27 will contain purified naphthalene since it should be as close as possible to the composition at the pure end of the column. The tank 24 at conduit 22 may contain naphthalene more impure than the feed since this is the impure end. 'The material in column 20 may be alternately heated and chilled whilethe run is being conducted. The material-in column 26 may be heated during each heating period by the introduction of a condensable gas into chamber 14 at a pressure high enough to cause it to condense therein at atemperature higher than the melting point of the material in the column.

The material in column 20 may bechilled during each cooling period by the introduction of a volatile liquid into chamber 15 at a pressure low enough to cause it to evap orate at a temperature lower than the melting point of the material in the column. At the end of each heating period, the liquid in column 20 may be cause to move a given distance towards pure end 19 of column 20 by the pumping of a given quantity, of liquid from tank 24 through conduit '22 via pump 25 into column 20 and by allowing liquid to flow into tank .27 through conduit 29. Conduit 29 may be at the bottom to prevent any air in tank 27 from entering column 20. At the end of each cooling period, the liquid in column 20 may be caused to move a given distance towards impure end 21 of column 20 by the pumping of a given quantity of liquid from column 29 into tank 24 through conduit 22 via pump 25. The thermal expansion and contraction of the contents of column 29 during the heating and cooling periods may-be compensated for by a flow of liquid in either direction through conduit 29 into or out of tank 27. Crude napthalene can be introduced into column 29 through conduit 11 at a constant controlled flow rate. Also, relatively pure product may be withdrawn from conduit 12 at a constantcontrolled flow rate, and relatively impure by-product at a constant controlled flow rate through conduit '13. Eductor conduits 30 are provided to allow the ingress and egress of air or inert gas into chamber 27 and 24. p

FIG. 6 illustrates another embodiment comprising a long column 26 having a major or pure end 19 and a minor or impure end 21. At pure end 19, chambers 23 and .24 are provided, chamber 24 being connected to the column via a two-way flow pump 25 and chamber 23 being connected via a two-way flow pump 28. A product withdrawal conduit :12 is provided at the pure end of column 2% which can lead to a proportioning pump 35 for controlling the rate of product withdrawal. A feed input conduit 11 is provided to connectthe central portion of the column 20 with a source of liquid feed which may be metered at a controlled flow rate by pump 36. Chamber 26 is connected with the impure end 21 of column 20 by means of a two-way pump 28 and chamber 27 by means of conduit 29. By-product withdrawal conduit 13 can connect the impure end of column 20 with a proportioning pump 37 suitable for effecting the controlled rate withdrawal ofby-product. Vent conduits 30 are provided for chambers-23,24, 26 and 27. Conventional heating and cooling means for column 20 and chambers 24 and 27 are not shown in FIG. 6. Also, the conventional apparatus for controlling the flow rate of the feed, the product and the by-product is not shown. When apparatus such as is shown in FIG. 6is operated, a run may be started by filling column 2!) and chambers 24 and 26 with a liquid feedmaterial such as an impure molten substance. .Also, chamber 27 may be partly filled with liquid feed before the run is started. The material in column 20 and chambers 24 and 27 may be alternately heated and chilled during the run by a system not shown in FIG. 6. At the end of each heating period after most of the solid material in the column has melted, liquid in column 20 can be caused to move a controlled distance towards the pure end 19 of the column by pumping a given volume of liquid from chamber 26 into column 241 and by pumping this same quantity of liquid from the other end 19 of column 20 into chamber 23. At the end of each cooling period, the remaining liquid in column 20 can be caused to-rnove a controlled distance towards the impure end 21 of the column by pumping a given quantityof liquid from chamber 23 into column 20 and by pumping the same given quantity of liquid from column 20 into chamber 26. During each cooling period, liquid may be pumped or transferred from chamber 24 into the pure end 19 of column 20 at a controlled flow rate such that the purity of the material in the freezing liquid-solid interface remains the same in a given part of the column during the cooling period. This desirable condition may be achieved by control of both the solidification rate of the contents of the column and the flow rate of liquid discharged into column 26 from pump 25. During each heating period, pump 25 may be off. At the end of each heating period the same amount of material that was transferred from chamber 24 into column 20 is transferred in the reverse direction. Surge chamber 27 serves to compensate for thermal expansion and contraction of the contents in column 20 and for the volume of material pumped into and out of chamber 24. Chambers 24, 23, 26 and 27 should be so positioned in space that no air or gas is transferred from any of them into column 29. Chambers 23, 24, 26 and 27 may all be provided with eductor conduits 30 if desired. The apparatus is preferably operated such that column 20 is completely filled at all times during the run. Of course, it shoud be understood that chambers 23 and 24 could be combined into one if desired.

FIG. 7 illustrates schematically one type of fractional sublimation column which is comprised of a number of relatively short conduits 24) which are connected in series by conduits 29. Each conduit 29 is provided with a valve 30. The central portion of the sublimation column is provided with a feed introduction conduit 11. The pure end 19 of the column 29 is provided with a product exit conduit 12 and the impure end 21 a by-product exit conduit 13. The means for heating and chilling the column 20 and the apparatus for controlling the flow rate of the feed, the product and the by-product are not shown in FIG. 7. The by-product conduit 13 and product conduit 12 are provided with valves 32 while the feed conduit is provided with valve 33.

When apparatus such as is shown in FIG. 7 is operated as a fractional sublimer, a run may be started by first opening all of valves 30, closing valves 32, heating column 20 to the temperature it normally obtains at the end of each heating period, and filling column 20 with feed gas to a pressure just below the vapor pressure of the feed at the starting temperature. Cold trap 23 may then be chilled sufliciently to enable it to fill with solid condensate. Every cycle conducted thereafter during the run may involve the following steps:

(1) All valves are closed;

(2) The columns 20 are chilled to a temperature such that approximately half of their gaseous contents condense;

(3) Valves 30 are opened after the cooling period;

(4) Cold trap 23 is heated sufficiently to vaporize its contents; at this same time cold trap 26 is chilled sufiiciently to cause it to become filled with solid condensate;

(5) All valves are closed;

(6) Columns 20 are heated to a high enough temperature to vaporize all of the condensate therein;

(7) All valves are opened; then a measured quantity of feed is introduced through the feed conduit 11; a measured quantity of product is withdrawn through product conduit 12; and a measured quantity of byproduct is withdrawn through by-product conduit 13.

In order to obtain a clearer understanding of the process aspects of the invention, the following description is given with respect to the various embodiments which may be carried out in accordance with the broadly defined method of fractional solidification.

FRACTIONAL FREEZING In utilizing fractional freezing as a method of segregating major and minor ingredients, Iprefer to carry out the method in such a manner that the ratio of the major to the minor ingredient is the same in the liquid and the solid phase of the major ingredient on the liquid-solid melting interface during the melting period at any given portion of the column as described hereinbefore.

In some cases my fractional freezing process may be I4 operated such that each cycle is operated in the following fashion:

(1) During the freezing period substantially all the liquid in the column may be frozen. Also, during the freezing period the liquid in the column may be moved towards the minor end of the column at a velocity proportional to the percentage of the material that is still liquid in the column. Therefore, at the end of the cool in; period the velocity of the liquid is much higher and the volume of the liquid much smaller than at the beginning of the period;

(2) During the melting period the liquid may be held substantially stationary;

(3) After the melting period the liquid may be moved back towards the major end of the column to substantially the same position that it occupied at the beginning of the cycle.

I prefer to operate a fractional freezer so that the material in the column is heated from one side or longitudinal element of the column during the melting periods and is' chilled from the other side or longitudinal element of the column during the freezing periods. This procedure results in the material being melted in inverse order to how it was frozen.

Any suitable method for heating and chilling the material in the fractional freezing column may be employed. Also, any suitable method for propelling the liquid through the column at a controlled rate during the flow periods may be employed.

My fractional solidification process may be operated as an autocrucible fractional freezing process or an autocrucible fractional crystallization process by containing the liquid material ofthe fractional freezing column in a trough-shaped skull of the same composition as the liquid. The top surface of the liquid may be exposed to either a vacuum or some suitable atmosphere. The skull must be thick enough to have its outside portions maintained at a low enough temperature to prevent it from being melted through by the hot liquid Within it. The outside surface of the skull may be cooled by natural heat loss, or by contact with a surface of a heat exchanger or by direct contact with some suitable coolant.

During each heating period, heat may be applied to the liquid material in the trough by such suitable heating means as a system of electron guns, electric induction heating, radiant heating or any other suitable heating method. In most cases, the heat may be applied to the liquid through its top surface. When the liquid in the trough is being heated, material melts or dissolves into it'from the skull containing it. Care must be exercised to avoid melting through the skull otherwise the liquid will run out of the trough at an uncontrolled rate or at an undesirable location. Also, care must be exercised not to melt or dissolve through the skull and contaminate the liquid therein with any foreign material which may be in contact with the skull.

During the major and the minor flow periods, the liquid can be caused to flow in the desirable direction by the force of gravity or by any other suitable means. Usually, the skull is maintained in a position such that the central axis of the top surface of the liquid pool contaiued within it is substantially horizontal during nonflow periods. However, the skull may be provided with means to tilt it slightly during flow periods to cause its liquid contents to flow at the desired rate towards either the major or the minor end of the column as the case may require.

In case in which may autocrucible fractional freezing process is operated on a continuous basis, the feed may be introduced into the central portion of the liquid pool while the product is decanted from the pure end and the by-product from the impure end. In such cases, gravity may be the force that propels the flow of feed to the ends of the column.

In cases in which the autocrucible fractional freezing 'met-hod is employed, the fractional freezing column may be defined as that portion of the skull which'is molten or in solution (in liquid phase) 'at' least some of the time during the run, the column the skull.

The rate at which the liquid leaves each end of the column may be controlled by the amount of heat applied to the lip over which the liquid pours. By melting or dissolving away a portion of the lip as required more liquid is caused to flow over it. I

7 After the autocrucible fractional solidification process has bee'n'operating for a long enough time to allow an equilibrium distribution ofimpurities to be achieved in the fractional solidification column, the distribution of impurities in the portion of the skull immediately adjacent to the side and bottom of the column may assume the same value as in the column at that point.

In some cases in which the autocrucible process is operated, the size of the column may be caused to be of liquid being supported by slightly larger during the first portion of the run in order that the slightly smaller column operated during the balance of the run may be contained in a skull of the same composition as itself at every point on the interface of the skull and the column. For example, in the autocrucible fractional freezing of aluminum, the cross section of the column during the first part of the run may be 20 cm. wide by 6 cm. deep and then the size of the column reduced to 18 cm. Wide by S cm. deep to leave a skull of 1 cm. thickness which has thesame concentra tion of impurities as the column at all points on the interface of the new column with the skull.

In some cases, such as when a mixture of hydrocarbon waxes is to be segregated into different melting point fractions, the process can be employed as a fractional freez ing process to split a mixture of waxes into fractions of dilferent melting points. This is analogousto the splitting of petroleum products into different boiling point fractions in a continuous fractional distillation tower in which fractions are withdrawn from different levels in the tower. When my fractional solidification process is employed to produce a number of difierent melting point fractions continuously, product Withdrawal conduits can be provided at'different points along the column at different distances from the feed point, Some of these product discharge points can lie in the low melting point section (impurity concentrating section) and'others may be located in the high melting point section (impurity stripping section). The further the product discharge conduit is from the feed conduit in the high melting point section, the higher would be the meltingpoint of the material withdrawn from it. Likewise, the further the product discharge conduit is from the feed point in the low melting point' section, the lower would be the melting point of the material withdrawn from it. When the, fractional freezing process is being employed to produce a number 7 of different melting point fractions, the impurity stripping section corresponds with the high melting point section and the impurity concentrating section with the low melting point section. Any material withdrawn from the low melting point section usually has a lower melting point than the feed. Also, any material withdrawn from any point in the high melting point section usually has a higher melting point than the feed. Any suitable number of withdrawal conduits may be provided in the low and the high melting point sections. In general, the further a given product or byproduct withdrawal conduit is from the feed conduit, the greater would be the difference in the melting point of the material withdrawn from it and the feed material. For example, if material were being withdrawn from a by-product conduit 100 meters and a second by-product conduit 200 meters from the feed conduit in the impurity stripping section, the melting point of the material being withdrawn from the first conduit would have a melting point nearer that of a conduit. In casesin which there are a number of product and by-product withdrawal conduits and the flow rate and the composition of the feed is constant, the melting point of material being withdrawn from any one given withdrawal conduit is going to be dependent not only upon the flow rate of material from it but from all the other conduits in the system. Usually, when a run is being conducted with a feed maten'al'of uniform composition, the flow rate of the feed and of the material from each of the withdrawal conduits is held constant to give fractions of definite melting point composition.

FRACTIONAL CRYSTALLIZATION PROCESS In carrying out the fractional crystallization process an important step is employed which is not required in the fractional freezing process. This step comprises adding solvent to the pure end of the column at a rate equal to the rate that the process causes solvent to travel from the major or pure end of'the column to the minor or impure end. If this step would not be done, any solvent present would migrate to the impure end of thecolumn and then the process would stop for lack of solvent.

This migration of the solvent towards the impure end of the column can be compensated for by evaporating solvent from the impure end of the column as fast as it is caused to arrive there, condensing the pure solvent in an area separate from the impurities, and introducing the pure condensate solvent to the pure end of the column. The addition of the pure solventto the pure end of the column also causes an increased flow of solution, which carries major ingredient in solution towards the impure end; thereby carrying majoringredient towards the impure end in the minor fiow periods as fast as it is carried towards the pure end during the major flow periods. The solvent moving through the column from the pure to the impure end aids in the transference of impurities towards the impure end, thereby leaving the major ingredient purer than it would be in many cases in which-the major ingredient would be purified by fractional freezing alone.

Fractional crystallization has the following advantages over fractional. freezing; g

(1) Materials can be purified by fractional crystallization at temperatures substantially below their melting point temperatures; therefore, many materials can be purified that are unstable at their melting point temperature or have excessively high melting points.

(2) The solvent that passes through the fractional crystallization column from the pureto the impure end of the column can cause some impurities to be removed that are almost equally soluble in the liquid and the solid phase of the major ingredientin cases in which the solvent is not present. V V t.

(3) In some cases, inwhich my fractional crystallization process is operatedas a batch-type process, the run may be divided into several major periods. During each period, a diiferent solvent may be caused to traverse from the pure to the impure, end of thecolumn. Each solvent may be employed as an aid in removing specific impurities. V V

In some .cases, my fractionahcrystallization process may be operated in thefollowing manner:

(l) A controlled flow rate of pure solvent may be added to the pure end of the column to compensate for the amount of solvent that theoperation of the process causes to travel to the impure end. i

(2) The very impure solution of major ingredient is withdrawn from the impure end of the column at the same rate'that the operation of the process causes it to arrive there.

(3) Enough major ingredient feed is introduced to the impure end .of the column to compensate for the rate that major ingredient migrates towards the pure end of the mn. t

(4) Note: Steps 2 and 3 can be combinedby evapor n elv m fwmth rs s de ast as it s there.

When my fractional crystallization process is operated, the concentration of the major ingredient in the solvent must be such that its crystallization temperature from the solution is higher than the freezing point temperature of the solvent from the solution. Also, the equilibrium ratio of the concentration of the minor ingredient to the major ingredient must be different in the liquid than in the solid phase of the major ingredient on the liquid-solid crystallization interface.

In some cases, my fractional crystallization process may be operated in the following manner:

(1) A substantially saturated solution of an impure major ingredient in a suitable volatile solvent may be contained in a horizontal column which has a gas space above the solution.

(2) Some of the major ingredient may be caused to crystallize out of solution by evaporating some of the solvent from the solution in the column. The evaporation of the solvent may be effected by reducing the pressure over the solution and may also be aided by heating the solution.

(3) The mother liquor left after the evaporation period is caused to flow a given distance towards the minor end of the column.

(4) After the minor flow period, the crystallized major ingredient may be caused to dissolve by adding an amount of solvent back into each unit length of the column equal to the amount evaporated from that unit length during the evaporation period.

(5) After the crystal dissolving period, a major flow period may be efiected in which the solution is transferred a distance towards the major end of the column such that the solution is back to the same location that it occupied at the beginning of the evaporation period.

In cases in which solvent is evaporated from the column during evaporation periods and is condensed or otherwise added to the column during condensation eriods, I prefer that the solvent be evaporated in such a manner that each unit mass of solution loses the same quantity of solvent during each evaporation period and gains the same amount of solvent during each condensation period. This desirable condition may be effected by having the cross section of the column substantially uniform, maintaining the depth of the solvent constant in all portions of the column, by maintaining the width of the solvent pool uniform, by maintaining the temperature of all portions of the solvent pool such that the vapor pressure of the solvent from all portions of the pool is thesame at any given time during the evaporation or condensation period, and by maintaining the partial pressure of the solvent in the atmosphere above the pool the same at any given time during the evaporation or condensation periods.

In cases where the coeflicient of solubility of the major ingredient in the solvent increases with increasing temperatures, the minor flow period of each cycle is conducted when the contents of the column are colder than during the major flow periods of each cycle. On the other hand, in cases where the coeflicient of solubility of the major ingredient decreases with increasing temperature, the minor flow period of each cycle is conducted when the contents of the column are hotter than during the major flow periods of each cycle.

As aforementioned, in cases where the ratio of the minor ingredient to the major ingredient in the liquid solution is higher than in the solid phase of the major ingredient on the liquid-solid crystallization interface, the pure end of the column corresponds with the major end and the impurities (minor ingredient) concentrated at the minor end of the column. In cases where the ratio of the minor ingredient to the major ingredient in the liquid solution is lower than in the solid phase of the major ingredient on the liquid-solid crystallization interface, the pure end of the colunm corresponds with the minor end and the impurities (minor ingredient) concentrate at the major end of the column.

Incaseswhere the coefficient of solubility of the major" ingredient increases with increasing temperature, the process may be operated in a cyclic fashion wherein'each cycle has:

('1) A minor flow period in which:

(a) The solution in the column is at a lower tem: perature than it is during the major flow period;

(b) The solution is caused to flow a given distance towards the minor end of the column; 7 (c) A higher percentage of the major ingredient in the column is in the crystallized state than during the major flow period. (2) A major flow period in which:

(a) The solution in the column is at a higher temperature than it is during the minor fiow'per'iod;' (b) The solution is caused to flow toward'the major end of the column a distance'such that it returns to essentially the same position that it occupied at the beginning of the minor flow period;

(c) A lower percentage of the major ingredient in" the column is in the crystallized state than during the minor fiowperiod.

In cases where the coefficient of solubility of the major ingredient decreases with increasing temperature,

the process may be operated in a cyclic'fashion'wherein each cycle has:

(a) The solution in the column is at a lower tem perature than it is during the minor flow period;

(b) The solution flows towards the major end of the column a distance such that it returns to essentially the same position that it occupied at the beginning of the minor flow period;

(c) A lower percentage of the major ingredient in the column is in the crystallized state than during the minor flow period.

In all cases, the average ratio of the concentration of the minor ingredient to the major ingredient in the solu-' tion during the minor flow period is different than it is during the major flow period.

As illustrative of this process, the following example relating to the purification of silver nitrate is given:

Example 1.-C0ntinu0us fractional crystallization of silver nitrate Two continuous fractional crystallizers of the same type and size may be provided. Each crystallizer may be similar in its general arrangement to the one shown in FIGS. 3 to 5 of the drawings. However, for the purposes of this illustration, reference is made toFIG. 6 which shows the general arrangementof the surge sham bers for the crystallizer.

Each crystallizer is constructed so that the silver nitrate solution is contained in a single continuous passage of, for example, 1,000 meters long by 2 centimeters wide by 5 centimeters deep; The passage is provided with cooling means for its topside and heating means for its bottom as is shown in FIGS. 3 to 5. The central longi-' tudinal axis of the passage is horizontal. Trichloro: monofluoromethane, hereinafter referred to as F-11, is employed as the refrigerant. A compressor is employed to take suction from the F-ll evaporization chambers =15 and discharge it as a gas into the condensation cham-. bers 14. Surge chambers 23 and 26 each have a capacity of 100,000 cc. Surge chamber 24 and likewise surge chamber 27 also have a capacity of 100,000 cc.

each. Means are provided for evaporating water from the silver. nitrate solutions in chambers 26 and 27, and

means are provided for admitting pure Water into chambers 23 and 24. In addition, means are provided for flowing liquid into or out of chambers 23, 24 and 26 at a controlled flow rate. The feed conduit is connected to the passage 300 meters from the impure end of the passage. A product withdrawal conduit is provided at the pure end of the passage and a by-product withdrawal conduit provided at the impure end of the passage. The feed conduit is provided with metering means for admitting liquid into the passage at a controlled flow rate. The product and the hy-product conduits are each provided with metering means for Withdrawing liquid at a controlled flow rate from the passage. Chambers 23, 24, 26 and 27 are each provided with heating and cooling means for heating and chilling the silver nitrate solution within'thern at the same rate that the silver nitrate solution in the passage is heated and chilled. The conduit that connects each chamber with the passage is located at a low enough levelto prevent any gas in any of the chambers from entering the passage at any time. Valves are provided in the conduit connecting each chamber with the passage.

Before the run is started, the passage 20 is filled with a saturated solution of silver nitrate in water at 80 C. The passage and the chambers are all heated to 80 C. Chamber 26 is then filled with more than sufiicient (more than 50,000 cc.) saturated silver nitrate solution at 20 C. to enable the solution in the passage to be flowed 50 meters towards the impure end during the minor flow period. Chamber 24 is filled with more than enough (more than 50,000 cc.) saturatedsolution 'at 80 C. to enable the solution in the passage to be moved approximately 50 meters towards the impure'end during the cooling period. At this point the apparatus is ready for the run to be started. 7

When the run is underway, a series of identical cycles may be effected. Each cycle in both fractional crystallizers may involve the following steps:

(1) Cooling period: During this period the contents of the passage and the chambers are cooled to 20 C. by evaporation of F-ll gas from chamber 15. Also, during this period, the contents of chamber 24 are flowed into the pure end of the passage 20 at such a rate that the average velocity of the liquid in the passage would be inversely proportional to the percentage of silver nitrate in the passage that is still in solution. The total amount of silver nitrate solution pumped from chamber 24 during the cooling period is such as to have caused a total average movement of 50 meters for the solution in the passage. During the cooling period the valves to chambers 23 and 26 are closed and the valve to chamber 27 is opened.

(2) Minor flow period: As soon as the temperature of the contents of the passage has reached 20 C. sufficient solution is transferred from chamber 23 into passage 20 to cause the cold solution in passage 20 to travel 50meters towards the impure end. During this period the valves to chambers 24 and 27 are closed.

' (3) Heating period: As soon as the minor flow period has been completed, the contents'of the passage and the chambers are heated to 80 C. by condensation of F-ll gas in chamber 14. Also, during this period the valves between the passage and chambers 26 and 27 are closed, and enough water evaporated from the silver nitrate solution in chambers 26 and 27 .to enable all the silver nitrate in each of them to be in the form of a saturated solution by the time the solution is heated to 80 C. In addition, the'same amount of water evaporated from chamber 27 maybe added to chamber 24 and the same amount of water evaporated from chamber 26 may be added to chamber 23. p 7

(4) Major flow period: At the conclusion of the heating period, the contents of chambers 26 are emptied into 20 the passage while the valves to chambers 2-4 and 27 are closed and the valve to chamber 23 is opened. Also, the contents of chamber 27 are emptied into the passage While the 'valves to chambers 23 and 26 are closed and the valve to chamber 24 is opened. After the major fiow period, 25,000 cubic centimeters of feed is introduced into the passage. During this introduction period, the valves to all the chambers are closed and the valves to the feed, product and the by-product conduits are opened. Approximately 20 times as much product as byproduct may be withdrawn at the same time the feed is introduced. After the feed has been admitted, the valves to the feed, product and by-product conduits are closed. The feed is comprised of an impure saturated solution of silver nitrate in water at 80 C.

After a number of cycles, the purity of the product and the impurity of the by-product would become constant.

The length of time for each cycle may be 15 minutes or any other length of time suitable for chilling and heating the contents of the chambers by the desired amount.

The two fractional crystallizers are operated in such a manner that the heating period of one corresponds with the cooling period of the other and vice versa. There fore, the F-ll being evaporated from the crystallizer being chilled could be condensed in the crystallizer being heated. This saves on electric power for the F-ll compressor.

It should be understoodthat many other specific embodiments of apparatus may be employed to accomplish substantially the same result as accomplished in the above example and that the above example is just a specific illustration of one method of conducting my fractional crystallization process.

FRACTIONAL SUBLIMATION PROCESS In utilizing this process in segregating two substances having different vapor pressures at a given temperature, it is essential that the temperature of treatment be maintained below the melting point of the major ingredient. Whether a batch :type or continuous process is used, I prefer that the apparatus along the lines illustrated in FlGf7 be employed;

In starting my process, I proceed as follows:

(1') Pump the air out of column 20;

(2)' 'Heat the column to the temperature to which it is heated at the end of each cycle;

- (3) Fill the column'with impure gaseous feed at a pressure just below its condensation temperature at the temperature of the heated column.

At this point the run may be started. During the run, the column undergoes a series of repeated cycles wherein each cycle is conducted in the following manner:

- (1) Cooling period: During this period the column is chilled to a temperature such that approximately onehalf of its gaseous contents condense. This causes the pressure in the column to drop approximately a half. The cooling is etfected in such a manner that there is a minimum o-ftransferpf gas in a direction parallel to the longitudinal central axis of the column. Such transfer may be minimized by cooling all portions of the column 'at a rate such that thevapor pressure of the condensate diminishes ata uniform rate in all portions of the column, or by having the column consist of a large number of separate chambers such as is shown in FIG. 7 which are closed off from one another during the cooling periods. (2): Minor flow period: At the end of the cooling period, a given quantity of gas may be either condensed at or withdrawn from the volatile (minor) end of the column and be generated in or injected into the non volatile (major) end of the column. The net result is that the gas in the column is transferred a given distance towards the volatile end. In cases in which the column consists of a series of chambers, the conduits that connect sponsor the chambers in-series are opened during thegas transfer periods.

(3) Heating period: After the minor flow period is completed, the column is heated to a temperature high enough to vaporize the condensate within it. This heating should be done in such a manner that there is a minimum of uncontrolled transfer of gas in a direction parallel to the central longitudinal axis of the column during the heating period. Such transfer may be minimized by either having the column consist of a large nurm ber of separate chambers which can be shut off from one another during the heating periods, or by heating the column in a manner such that the vapor pressure of the condensate in all portions of the column-increases at the same rate.

(4) Major flow period: At the end of the heating period, a given quantity of gas, which should be substantially equal to the amount of gas withdrawn from the volatile end during the minor flow period, may be either condensed at or be withdrawn from the non-volatile end of the column. Also, during this period this same quantity of gas should be generated in or injected into the volatile end of the column. The net result is that the gas in the column is transferred a given distance towards the non-volatile end. In cases where the column consists of a series of chambers, the passages that connect the chambers are open during the gas transfer period.

In cases where the process is operated on a batch-type basis, the volatile ingredient reaches an ultimate distribution with respect to the relatively non-volatile ingredient after a certain number of cycles. The relatively volatile ingredient tends to concentrate in the volatile end (minor end) of the column and the relatively non-volatile ingredient tends to concentrate in the non-volatile (major) end. The degree of possible ultimate segregation of two given ingredients may be increased by increasing the length of the column and by decreasingthe length of the stroke of the motion of the gas in each gas transfer period.

The sublimation process may also be operated in the following fashion:

(1) The fractional solidification column may be fabricated of a collapsible material such as plastic or be designed such that its volume may be changed at will.

(2) Means may be provided to apply a controlled pressure into the collapsible column in such a manner that the gas in the column may be compressed at will.

Each cycle of operation may involve the following procedure:

(1) Compression period: At the start of each cycle, the column may be completely filled with gas at a relatively low pressure. Sufiicient pressure may be applied to the outside of the collapsible column to cause approximately one half of the gas to condense.

(2) Minor flow period: During the minor flow period, conditions of temperature and pressure in the column should be such that substantially no condensate evaporates or gas condenses. The controlled motion of gas towards the minor end of the column may be effected by admitting a given quantity of gas into the major end of the column and by withdrawing this same given quantity of gas from the minor end. Also, during the minor flow period the volume and shape of the column should be held constant.

(3) Decompression period: During this period the pressure applied to the contents of the column is diminished to an extent such that approximately all the solid condensate flashes into gas phase.

(4) Major flow period: During this period conditions of temperature and pressure in the column should be'such that substantially no material condenses or vaporizes. The controlled motion of the gas in the column towards the major end may be effected by admitting a given quantity of gas to the minor end and withdrawing a given quantity of gas from the major end. At the conclusion 22 of the major flow period the position of the body of gas in the column should be the same as at the beginning of the compression period. Also, during the major flow period, the volume and shape of the column should be constant.

The compression version of my fractional sublimation process may be operated in an adiabatic fashion in which the effect of a change in pressure alone causes material to be'condensed or vaporized. When the process is so operated the time per cycle may be very short, the shortness of which would be limited by mechanical considerations only. For example, it is possible for each cooling period or heating period to be only one tenth of a second in duration. In cases Where the fractional sublimation process is operated as an adiabatic process, the pressure in the column should be maintained substantially constant during the major and the minor flow periods.

The compression version of my fractional sublimation process may also be operated under conditions in which at least some of the heat of condensation of the material condensing in the compression periods is absorbed by solid material of a different composition than that of the material being processed. This solid material may be the Walls of the column and perhaps solid packing materialsuchas heavy steel wool'in the column. The packing serves to provide a large surface area on which the gas-may condense and also may serve as a heat sink for the heat of sublimation. When material condenses on the solid packing much of the heat of condensation can be absorbed into the packing. When material is being vaporized much of the heat of vaporization may be supplied. by the packing. The packing may be in many suitable forms such as steel wool, glass wool, multiple layers of screening, perforated metal plates spaced at given distances. apart, Raschig rings, metal turnings, and many other forms. The packing is contemplated as being stationary.

The collapsible column employed in the compression version of my fractional sublimation process may be in any suitable form which allows the total volume of the column to be changed at will. The column should be designed so that the rate of change of volume in the compression and decompression periods is substantially uniform in all portions of the column. For example, if the column is shrinking 10% in volume per second during the compression period, the space defined by any two planes normal to the longitudinal central axis of the column would be shrinking at the same rate. The reason for this requirement is to minimize the movement of gas in the column duringthe compression and the decompression periods.

I prefer to operate my fractional sublimation process in a manner that causes all the material being processed in the apparatusto be in the gas phase during the major flow periods.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the in.- vention, as those skilled in the art will readily understand. Such modifications and variationsware considered to be within the purview and scope of the invention and the appended claims.

What is claimed is:

1. The method of segregating by fractional solidification at least one ingredient from a material composed of at least one major and one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material differs from that in a fluidized portion which comprises establishing acolumn of said material, said column having a minor end towards which a minor ingredient may be segregated duringa minor flow period and a major end towards which a major ingredient may be segregated during a major flow period; subjecting said material to atreating cycle having at least one solidification period and one fluidization period per cycle, wherein the fluid material in the column is moved towards the minor end of the column during a minor flow period while at least a portion of the major ingredient is in the solid state and wherein the material in the fluid state is moved towards the major end of the column during a major flow period while a larger portion of the major ingredient is in the fluid state; and continuing said treatment via a series of repeated cycles having at least one minor flow period and one major flow period in each cycle, thereby to segregate at least one minor ingredient at one end of the column while segregating the major ingredient at the other end.

2. The method of segregating by fractional solidification at least one ingredient from a material composed of at least one major and one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material difiers from that in a fluidized portion which comprises establishing a column of said material, said column having a minor end towards which a minor ingredient may be segregated during a minor flow period and a major end towards which a major ingredient may be segregated duping a major flow period; subjecting said material to a treating cycle having at least one solidification period and one fluidization period per cycle, wherein the fluid material in the column is moved towards the minor end of the column during a minor flow period in which a relatively small portion of the material being processed is in the fluid state and wherein the material in the fluid state is moved towards the major end of the column during a major flow period in which a relatively larger portion of the material being processed is in the fluid state; and continuing said treatment via a series of repeated cycles having at least one minor flow period and one major flow period in each cycle, thereby to concentrate at least one minor ingredient at one end of the column while concentrating the major ingredient at the other end.

3. 'The method of claim 2, wherein feed material is added to the column at a point intermediate the major and minor ends of the column, wherein relatively pure major ingredient withdrawn from the major end of the column, and wherein relatively concentrated minor ingredient is withdrawn from the minor end of the column.

4. The method in accordance with claim 2, wherein heat is extracted from the column of material during solidification periods and wherein heat is added to the column during the fluidiza-tion periods. 7

5. The method in accordance with claim 2, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coefiicient of solubility in the solvent that increases with increasing temperature, wherein heat is extracted from the column a during the solidification periods, and wherein heat is added to the column during the fluidization periods, whereby the major ingredient is segregated firom said minor ingredient.

6. The method in accordance with claim 2, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coeflicient of solubility in the solvent that decreases with increasing temperature, wherein heat is added to the column during the solidification periods, and wherein heat is' extracted from the column during the fiuidization periods, whereby the major ingredient is segregated from said minor ingredient.

7. The method in accordance with claim 2, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a different vapor pressure than the minor ingredient, wherein heat is withdrawn from the column during the solidification periods, and wherein heat is added to the column during the fln-idization periods, whereby said major ingredient is segregated from said minor ingredient.

24 8. The method in accordance with claim 2, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a different vapor pressure than the minor ingredient, increasing the pressure of the material in the column during the solidification periods and wherein the pressure of the material is decreased in the column during the fluidization periods, whereby said major. ingredient is segregated from said minor ingredient.

9. The method in accordance with claim 2, wherein the velocity of the fluid material in the column during the fluidization periods is maintained such that the ratio of the major ingredient to the minor ingredient in the fluid and the solid phase of the major ingredient on the fluidsolidrfluidization interface is substantially the same at any given point in the column.

10. The method in accordance with claim '9, wherein the velocity of the fluid material in the column is different during the solidification periods than during the fluidiziation periods.

11. The method in accordance with claim 2, as applied to fractional freezing and fractional crystallization, wherein the column of material being processed is contained in a chilled autocrucible skull of substantially the same composition as the material being processed.

12. The method in accordance with claim 11, wherein the liquid pool of material being processed is exposed and wherein the liquid material is caused to move by the force of gravity during the liquid fiow periods.

:13. The method in accordance with claim 11, wherein feed material is added to the column at a point intermediate the major and the minor end of the column, wherein relatively purified major ingredient is withdrawn from the major end of the colunm, and wherein relatively concentrated minor ingredient is withdrawn from the minor end of the column.

14. The method of segregating by fractional solidification at least one ingredient from a material composed of at least one major and one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material differs from that in a fluidized portion which comprises establishing a column of said material, said column having a minor end towards which a minor ingredient may be segregated during a minor flow period and a major end towards which a major ingredient may be segregated during a major flow period; subjecting said material to a treating cycle having at least one solidification period and one fluidization period per cycle; moving the fluid material in the column during the solidification period towards the minor end of the column 'at a rate such that the ratio of minor ingredient to major ingredient in the solid phase of the major ingredient on the fluid-solid interface in any given portion of the column remains substantially the same during the entire solidification period; moving the remaining fluid at the end of the solidification period towards the minor end to a distance such that at the conclusion of the movement the ratio of the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface; maintaining the fluid m-ajor ingredient stationary-during the fluidization period; moving the fluid major ingredient towards the major end'of the'column a distance such that its position is the same as at the beginning of the solidification period, and continuing said treatment via a series of repeated cycles having at least one minor flow period and one major flow period in each cycle, thereby to concentrate at least one minor ingredient'at one end of the column while concentrating the major ingredient at the other end.

15. In the method in accordance with claim 14, fluidizing the material during each fluidizing period in an order inverse to that in which ill W38 solidified in the preceding solidification period.

16. In the method in accordance with claim 14, 'ex- 25 tracting heat from one side of the column during the solidification periods, supplying heat to the opposite side of the column during the fluidization periods, thereby to fluidize the material during each fluidization period in inverse order to how it was solidified in the preceding solidification period.

17. The method of claim 14, wherein feed material is added to the column at a point intermediate the major and minor end of the column, wherein relatively purified major ingredient is withdrawn from the major end of the column, and wherein relatively concentrated minor ingredient is withdrawn from the minor end of the column.

18. The method in accordance with claim 14, wherein heat is extracted from the column of material during solidification periods and wherein heat is added to the column during the fluidization periods.

19. The method in accordance with claim 14, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coeflicient of solubility in the solvent that increases with increasing temperature, wherein heat is extracted from the column during the solidification periods, and wherein heat is added to the column during the fluidization periods, whereby the major ingredient is segregated from said minor ingredient.

20. The method in accordance with claim 14, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coeflicient of solubility in the solvent that decreases with increasing temperature, wherein heat is added to the column during the solidification periods, and wherein heat is extracted from the column during the fluidization periods, whereby the major ingredient is segregated from said minor ingredient.

21. The method in accordance with claim 14, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a diiferent vapor pressure than the minor ingredient, wherein heat is withdrawn from the column during the solidification periods, and wherein heat is added to the column during the fluidization periods, whereby said major ingredient is segregated from said minor ingredient.

22. The method in accordance with claim 14, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a different vapor pressure than the minor ingredient, increasing the pressure of the material in the column during the solidification periods and wherein the pressure of the. material is decreased in the column during the fluidization period-s, whereby said major ingredient is segregated from said minor ingredient.

23. The method in accordance with claim 14, wherein the velocity of the fluid material in the column during the fluidization periods is maintained so that the ratio of the major ingredient to the minor ingredient in the fluid and the solid phase of the major ingredient'on the fluidsollid fluidization interface remains-substantially the same on any given point of said interface during a given fluidization period.

24. The method in accordance with claim 23, wherein the velocity of the fluid material in the column is different during the solidification periods than during the fluidization periods.

25. The method in accordance with claim 14, as applied to fractional freezing and fractional crystallization, wherein the column of material being processed is contained in a chilled autocrucible skull of substantially the same composition as the material being processed.

26. The method in accordance with claim 25, wherein the liquid pool of material being processed is exposed and wherein the liquid material is caused to move by the force of gravity during the liquid flow periods.

27. The method or segregating at. least one ingredient 26 of one ingredient in a solidified portion of the material differs from that in a fluidized portion which comprises establishing a column of said material, said column having a minor end towards which a minor ingredient may be segregated during a minor flow period and a major end towards which a major ingredient may be segregated dur ing a major flow period, subjecting said material to a treating cycle having at least one solidification period and one fluidization period per cycle, maintaining the fluid major ingredient stationary in the column during the solidification period, moving the remaining fluid at the end of the solidification period towards the minor end of the column to a distance such that at the conclusion of movement the ratio of the concentration of the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface, subjecting the column to a fluidizing period during which fluid is moved towards the major end of the column at a rate such that the ratio of the minor ingredient remains substantially the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface, moving back the fluid major ingredient at the end of the fiuidizing period towards the minor end of the column a distance such that its position is the same as at the beginning of the solidification period, and continuing said treatment via series of repeated cycles having at least one minor flow period and one major flow period in each cycle, thereby to segregate at least one minor ingredient at one end of the column while segregating the major ingredient at the other end.

28. In the method in accordance with claim 27, fluidizing the material during each fluidization period in an order inverse to that in which it was solidified in the preceding solidification period.

29. The method of claim 27, wherein feed material is added to the column at a point intermediate the major and minor end of the column, wherein relatively enriched major ingredient is withdrawn from the major end of the column, and wherein relatively concentrated minor ingredient is withdrawn from the minor end of the column.

30. The method in accordance with claim 27, wherein heat is extracted from the column of material during solidification periods and wherein heat is added to the column during the fluidization periods.

31'. The method in accordance with claim 27, wherein the major ingredient is a solute dissolved in a suitable solvent, said maj'oringrcdient having a coeflicient of solufrom a material composed of at least one major and one bility in the solvent that increases with increasing temperature, wherein heat is extracted from the column during the solidification periods, andwherein heat is added to the column during the fluidization periods, whereby the major ingredient is segregated from said minor ingredient.

32. The method in accordance with claim 27, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coeflicient of solubility in the solvent that decreases with increasing temperature, wherein heat is added to the column during the solidification periods, and wherein heat is extracted from the column during the fluidization periods, whereby the major ingredient issegregated from said minor ingredient.

33. The-method-in accordance with claim 27, wherein the material in the fluid state is in the gaseous'phase whose major ingredient has a different vapor pressure than the minor ingredient, wherein heat is withdrawn from the column during the solidification periods, and wherein heat is added to the column during the fluidization periods, whereby said major ingredient is segregated from said minor ingredient.

34. The method in accordance with claim 27, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a difierent vapor pressure than the minor ingredient, increasing the pressure of the material in the column during the solidification periods and wherein the pressure of the material is decreased in the column during the fluidization periods, whereby said major ingredient is segregated from said minor ingredient.

i. 35. The method fin accordance with claim 27, wherein the velocity of the fluid material in the column during the fluidization periods is maintained such that the ratio of the major ingredient to the minor ingredient in the fluid and the solid phase of the major ingredient on the fluid-solid fluidization interface remains substantially the same on any given point of said interface during a given fluidization period. 7

36. The method in accordance with claim 35, wherein the velocity of the fluid material in the column is diflerent during the solidification periods than during the fluidization periods.

37. The method in accordance with claim 27, as applied to fractional freezing and fractionalcrystallization, wherein the column of material being processed is contained in a chilled autocrucible skull of substantially the same composition as the material being processed.

38. The method in accordance with claim 37, wherein the liquid pool of material being processed is exposed and wherein the liquid material is caused to move by the forceof gravity during the liquid flow periods.

39. The method of segregating at least one ingredient from a material composed of at least one major and one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material differs from that in a fluidized portion which comprises establishing a column of said material, said column having a minor end towards which a minor ingredient may be segregated during a minor flow period and a major end towards which a major ingredient may be segregated during a major flow period, subjecting said material to a treating cycle having at least one solidification period and one fluidization period per cycle, moving the fluid major ingredient towards the minor end of the column at a controlled rate during the solidification period, moving the remaining fluid at the end of the solidification period towards the minor end ofthe column a distance such that at the conclusion of movement the ratio of the concentration of the minor ingredient to the major ingredient is substantially the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface, subjecting the column to a fluidizing period during which the fluid major ingredient is moved towards the major end of the column at a rate such that the ratio of the minor ingredient to the major ingredient is the same in the fluid and the solid phase of the major ingredient at any given point on the fluid-solid interface, moving the fluid at the end of the fluidizing period in a direction in the column such that its position is the same as at the beginning of the solidification period and continuing said treatment via a series of repeated cycles having at least one minor flow period and one major flow period in'each cycle, thereby to segregate at least one minor ingredient at one end of the column while segregating the major ingredient at the other end.

, 40. The method of claim 39, wherein feed material is added to the column at a point intermediate the major and minor end of the column, wherein relatively enriched major ingredient is withdrawn from the major end of the column, andwherein relatively concentrated minor ingredient is withdrawn from the minor end of the column.

41. In the method in accordance with claim 39, fluidizing the material during each fluidization period in an order inverse to that in which it was solidified in the preceding solidification period. j

42. The method in accordance with. claim 39, wherein heat is extracted from the column of material during solidification periods and wherein heat is added to the column during the fluidization periods.

43. The method in accordance with claim 39, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coefficient of solubility in the solvent that increases with increasing temper- 28 the column during the fluidization periods, whereby the major ingredient is segregated from said minor ingredient.

44. The method in accordance with claim 39, wherein the major ingredient is a solute dissolved in a suitable solvent, said major ingredient having a coefiicient of solubility in the solvent that decreases with increasing temperature, wherein heatis added to the column during the solidification periods, and wherein heat is extracted from the column during the fluidization periods, whereby the major ingredient is segregated from said minor ingredient.

45. The method in accordance with claim 39, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a different vapor pressure than the minor ingredient, wherein heat is withdrawn from the column during the solidification periods, and wherein heat is added to the column during the fluidization periods, whereby said major ingredient is segregated from said minor ingredient.

46. The method in accordance with claim 39, wherein the material in the fluid state is in the gaseous phase whose major ingredient has a different vapor pressure than the minor ingredient, increasing the pressure of the material in the column during the solidification periods and wherein the pressure of the material is decreased in the column during the fluidization periods, whereby said major ingredient is segregated from said minor ingredient.

47. The method in accordance with claim 39, wherein the velocity of the fluid material in the column during the fluidization periods is maintained so that the ratio of the major ingredient to the minor ingredient in the fluid and the solid phaseof the major ingredient on the fluid-solid fluidization interface is substantially the same on any given point of said interface.

48. The method in accordance with claim 47, wherein the velocity of the fluid material in the column is diflerent during the solidification periods than during the fluidization periods.

49. The method in accordance with claim 39, as applied to fractional freezing and fractional crystallization, wherein the column of material being processed is contained in a chilled autocrucible skull of substantially the same composition as the material being processed.

50. The method in accordance with claim 49, wherein the liquid pool of material being processed is exposed and wherein the liquid material is caused to move by the force of gravity during the liquid flow periods.

51. An apparatus for refining material containing a major ingredient and at least one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material diflers from that in a fluidized portion which comprises a column defining an elongated chamber for receiving such material to be treated, said column having a major end adapted to collect the major ingredient and a minor end adapted to collect the minor ingredient, means associated with said column for solidifying a portion of the material during a step of a treating cycle and means for fluidizing the material during another step of said cycle, a fluid coupling means associated with the major end of the column, a fluid coupling means associated with the minor end of the column, fluid driving means associated with each of said coupling means, so that when using said fluid coupling means during a treatment step the material in the fluid state in the column is caused to move in one direction at a time in each cycle in which a relatively high percentage of the material being treated in the column is in the fluid state, and in the opposite direction at a time in each cycle in which a relatively smaller percentage of said material is in the fluid state.

52.. The apparatus of claim 51, wherein feeding means are provided at a point of the column intermediate the ends for feeding material thereto and wherein discharge means are provided at the major and minor ends of the column for discharging major and minor ingredients therefrom.

53. An apparatus for refining by fractional freezing material containing a major ingredient and at least one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material differs from that in a fluidized portion which comprises a column defining an elongated chamber for receiving such material to be treated, said column having a major end adapted to collect the major ingredient and a minor end adapted to collect the minor ingredient, means for heating said column along a longitudinal element thereof, means for cooling said column along another longitudinal element thereof, said heating and cooling means being adapted to eflect at least one solidification and one fluidization period per cycle of treatment, a fluid coupling means associated with the major end of the column, a fluid coupling means associated with the minor end of the column, fluid driving means associated with each of said coupling means, so that when using said fluid coupling means during a treatment step the material in the fluid state in the column is caused to move in one direction at a time in each cycle in which a relatively high percentage of the material being treated in the column is in the fluid state, and in the opposite direction at a time in each cycle in which a relatively smaller percentage of said material is in the fluid state, whereby when the material is returned to substantially its original position, the major end of the column is enriched in major ingredient and the minor end of the column is enriched in the minor ingredient.

54. The apparatus of claim 53, wherein feeding means are provided at a point of the column intermediate the ends for feeding material thereto and wherein discharge means are provided at the major and minor ends of the column for discharg ng major and minor ingredients therefrom.

55. An apparatus for refining by fractional crystallization material containing a major ingredient and at least one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material differs from that in a fluidized portion which comprises, a column defining an elongated chamber for receiving a solution to be treated, said column having a major end adapted to collect the major ingredient and a minor end adapted to collect the minor ingredient, means associated with said column for effecting crystallization of a portion of the contained major ingredient during a step of a treating cycle and for fluidizing said ingredient during another step of said cycle, a fluid coupling means associated with the major end of the column for adding solvent to said material, a fluid coupling means associated with the minor end of the column for removing solvent from this material, fluid driving means associated with each of said coupling means, so that when using said fluid coupling means during a treatment step the material in the liquid state in the column is caused to move in one direction at a time in each cycle in which a relatively high percentage of the material being treated in the column is in the fluid state, and in the opposite direction at a time in each cycle in which a relatively smaller percentage of said material is in the fluid state, whereby when the material is returned to substantially its original position in the column the major end of the column is enriched in major ingredient and the minor end of the column is enriched in minor ingredient.

56. The apparatus of claim 55, wherein feeding means are provided at a point of'the column intermediate the ends for feeding material thereto and wherein discharge means are provided at the major and minor ends of the column for discharging major and minor ingredients therefrom.

57. An apparatus for refining by fractional sublimation a gaseous material containing a major ingredient and at least one minor ingredient characterized in that the concentration of one ingredient in a solidified portion of the material difiers from that in a fluidized portion which comprises a column defining an elongated chamber for receiving such material to be treated, said column having a major end adapted to collect the major ingredient and a minor end adapted to collect the minor ingredient, means associated with said column for sublimating a portion of the contained major ingredient during a step of a treating cycle and for condensing the sublimated ingredient during another step of said cycle, a fluid coupling means associated with the major end of the column, a fluid coupling means associated with the minor end of the column, said coupling means having associated therewith means for effecting gaseous flow from the coupling means into the column, so that when using said fluid coupling means during a treatment step the material in the fluid state in the column is caused to move in one direction after sublimation and during another treatment step is caused to move in the opposite direction after condensation, whereby when the material is returned to substantially its original position in the column the major end of the column is enriched in major ingredient and the minor end of the column is enriched in minor ingredient.

58. The apparatus of claim 57, wherein feeding means are provided at a point of the column intermediate the ends for feeding material thereto and wherein discharge means are provided at the major and minor ends of the column for discharging major or minor ingredients therefrom.

References Cited in the file of this patent Pfann: Zone Melting, Apr. 18, 1958, pp. to 139. 

1. THE METHOD OF SEGREGATING BY FRACTIONAL SOLIDIFICATION AT LEAST ONE INGREDIENT FROM A MATERIAL COMPOSED OF AT LEAST ONE MAJOR AND ONE MINOR INGREDIENT CHARACTERIZED IN THAT THE CONCENTRATION OF ONE INGREDIENT IN A SOLIDIFIED PORTION OF THE MATERIAL DIFFERS FROM THAT IN A FLUIDIZED PORTION WHICH COMPRISES ESTABLISHING A COLUMN OF SAID MATERIAL, SAID COLUMN HAVING A MINOR END TOWARDS WHICH A MINOR INGREDIENT MAY BE SEGREGATED DURING A MINOR FLOW PERIOD AND A MAJOR END TOWARDS WHICH A MAJOR INGREDIENT MAY BE SEGREGATED DURING A MAJOR FLOW PERIOD, SUBJECTING SAID MATERIAL TO A TREATING CYCLE HAVING AT LEAST ONE SOLIDIFICATION PERIOD AND ONE FLUIDIZATION PERIOD PER CYCLE, WHEREIN THE FLUID MATERIAL IN THE COLUMN IS MOVED TOWARDS THE MINOR END OF THE COLUMN DURING A MINOR FLOW PERIOD WHILE AT LEAST A PORTION OF THE MAJOR INGREDIENT IS IN THE SOLID STATE AND WHEREIN THE MATERIAL IN THE FLUID STATE IS MOVED TOWARDS THE MAJOR END OF THE COLUMN DURING A MAJOR FLOW PERIOD WHILE A LARGER PORTION OF THE MAJOR INGREDIENT IS IN THE FLUID STATE, AND CONTINUING SAID TREATMENT VIA A SERIES OF REPEATED CYCLES HAVING AT LEAST ONE MINOR FLOW PERIOD AND ONE MAJOR FLOW PERIOD IN EACH CYCLE, THEREBY TO SEGREGATE AT LEAST ONE MINOR INGREDIENT AT ONE END OF THE COLUMN WHILE SEGREGATING THE MAJOR INGREDIENT AT THE OTHER END. 